Internal combustion (IC) engines are used throughout the world and mainly for motor vehicles. IC engines account for one of the largest consumers of petroleum products known. Due to the large amount of petroleum products consumed by IC engines and the gases exhausted from IC engines, numerous regulatory agencies have implemented regulations or are in the process of implementing regulations that require minimum average fuel economy of vehicles as well as limit the amount of pollutants that are exhausted from vehicles.
Earlier attempts at reducing vehicle emissions have centered on exhaust gas treatments. For example, earlier attempts have introduced reagents into the exhaust gas stream prior to the gas passing through a catalyst in order to effect selective catalytic reduction (SCR) of the nitrogen oxides (NOx) in the exhaust gases. Additionally, many vehicles now include exhaust gas recirculation (EGR) systems to recirculate at least some of the exhaust gases. Although EGR reduces the harmful emissions of vehicles, it also often reduces the vehicle's fuel economy.
The uses of SCR and EGR have been effective in reducing the emission problems in the exhaust stream, but have done little in improving the fuel economy and fuel consumption of vehicles. With the tighter regulations that are being implemented, many manufacturers have turned their focus to increasing the fuel economy of IC engines. It is generally known that only about thirty to forty percent of the energy produced by the fuel combustion of IC engines translates to mechanical power. Much of the remaining energy is lost in the form of heat. Therefore, one particular area of focus in the motor vehicle industry has been to recover some of the heat that is generated by the IC engine using a waste heat recovery system that converts heat into mechanical energy with, for example, a Rankine cycle.
Waste heat recovery systems typically use a working fluid, such as water, to recover the waste heat from the engine. Other fluids, such as ethanol, may also be used due to properties such as heat transfer or vapor pressure properties. Evaporators are typically used to transfer heat from the exhaust to the working fluid. The heat may convert the working fluid to a gas. The gas may then be conveyed to an expander where the heat is converted into mechanical energy.
However, heat transfer to the working fluid may not always be desirable. For example, heat transfer to the gas that is contained by an obstruction in the waste heat recovery system may not be desirable. Transferring heat to contained gas can cause an undesirable level of pressure that could cause damage to the evaporator or a condenser in the waste heat recovery system. Additionally, transferring heat from the exhaust system to the working fluid may not be desirable when the engine is heating up the exhaust system. For example, transferring heat from the exhaust system will increase the time it takes the engine to heat the exhaust system. Heat transfer to the working fluid can be reduced or eliminated by limiting or preventing exhaust flow to the evaporator. Accordingly, there is a need to limit or prevent exhaust flow to the evaporator.